1. Technical Field
The present invention relates to a powder blast tool for mixing a powder with a pressurised gas, a powder reservoir suitable for this purpose, an insert suitable for this powder reservoir, a method of dental treatment, and a preferred use of the powder blast tool or of the method according to the invention.
2. Background Art
Powder blast tools or dental abrasive blast tools, in which a dental powder stored in a reservoir is supplied together with a gaseous carrier medium at a nozzle arrangement of a handset connected via a discharge line, in general being mixed with pressurised water, are known for example from EP 1 243 226 A2. Therein, a preferably exchangeable powder reservoir is so fixed to a powder blast tool that a quantity of powder stored in the powder reservoir is continuously transferred into a mixing chamber, the powder is mixed with the air stream passing through the mixing chamber and is supplied as a powder-air mixture to a handset and a discharge nozzle disposed thereon for the dental treatment. EP 0 097 288 B1 discloses a generic powder blast tool with a powder reservoir into which a pressurised gas is introduced, so that the powder therein is swirled and can be discharged via an outlet aperture as a powder-air mixture. The powder reservoir is in this case located in the powder blast tool and can be refilled with powder from the top each time.
EP 1 159 929 A2 discloses a powder blast tool with a powder reservoir and an additional exchangeable fluid reservoir, with which e.g. de-mineralised water can be supplied to the teeth as a flushing fluid. The powder blast tool in this case has the same configuration in principle as the tool according to EP 0 097 288 B1, i.e. the powder reservoir is permanently incorporated in the powder blast tool.
From EP 0 268 948 B1, a sealing device for a fluid reservoir is known. The sealing device is formed for screwing the fluid reservoir on to a mounting part, which is provided on the exterior of the powder blast tool. Thus the fluid reservoir can be mounted exchangeably on exterior of the powder blast tool.
From U.S. Pat. No. 1,664,369 it is known that the powder supplied in a powder reservoir is mixed in a metered manner with the gaseous carrier medium by means of a motor-driven conveyor screw. The conveyor screw is in this case disposed under an outlet aperture of the powder reservoir. The powder is mixed with the gas at the end of the conveyor screw.
From EP 0 119 735 B2, a powder reservoir is known in whose centre an elongate tube is incorporated, which has at the lower end two inlet apertures, through which on the one hand pressurised gas and on the other hand powder can enter, which is stored in the powder chamber and surrounds the elongate tube, the powder being carried along by the inflowing gas inside the elongate tube and upward, mixed with the gas, and discharged at the upper end of the powder reservoir via an outlet aperture.
The prior powder blast tools or the powder reservoirs and nozzle arrangements or inserts for powder reservoirs suitable for the same have various disadvantages. A powder reservoir permanently installed in the powder blast tool has the disadvantage that this can only be cleaned together with the tool itself and aseptic cleaning of the interior of the powder reservoir is barely possible. Furthermore, the powder reservoir always has to be refilled, i.e. the closures, seals etc. connected to the reservoir get dirty over time, so that the entire powder blast tool becomes unusable. Furthermore, the known powder blast tools have the disadvantage that these are suitable only for a certain type and grade of powder, i.e. if smaller or larger grain sizes are used for the powder or different powder compositions are used, the corresponding supply and nozzle arrangements are not suitable, so that either too much or too little powder is supplied together with the gas jet. If fine-grained powder is used with a grain size of less than 100 μm, in EP 0 119 735 B2 there is the risk that the air supply line may become blocked with powder.
Also, for a certain powder blast tool only very particular powder reservoirs can be used, which are matched exactly to the conveying or nozzle arrangement of the powder blast tool. Also the known conveying quantity of powder-gas mixture can only be modified by a change in pressure of the gas being supplied or a change in the supply of powder, the powder supply generally being dependent on the speed of the gas, i.e. the gas pressure and the corresponding nozzle arrangement.